This invention relates to a method for rotary well drilling that makes it possible to actively control both the inclination and the azimuth path of the well when drilling. The invention also relates to a device for implementing said method.
The techniques that aim at controlling the direction of the drilled well""s path, when drilling a well, have known spectacular progress with the advent of measurements at the bottom of the hole during the drilling (techniques called MWD, from xe2x80x9cMeasurement While Drillingxe2x80x9d). The inclination and azimuth orientation of the drilling can thus easily be followed and controlled, using both traditional deflection systems, such as the downhole motor hooked up to a bent sub (called xe2x80x9cmotor and bent-subxe2x80x9d) or, more recently, the downhole motor with built-in sub (called xe2x80x9cbent-housingxe2x80x9d).
Said downhole motor drilling systems, and mainly the last one mentioned above, which is widely used today, have taken on a more and more important role among the array of directional tools being used in modem directional drilling operations. Over the last few years, they even had a tendency to supersede the directional tools that use the traditional rotary drilling principle.
However, downhole motor drilling does have a certain number of disadvantages.
The principle is linked to the fact that, in order to make corrections to the path, it is necessary to keep rotating the stopped string, so as to be able to point the downhole motor bend in a defined direction in a fixed plane. Stopping the rotation of the string leads to a significant increase in the friction of the drill string inside the well which has a negative effect on, among other things, the correct transmission of the weight over the drill bit needed for the drilling to progress properly. Therefore, the speed of penetration is reduced, as is the possible length of the drilling passes, whether it be in traditional deviated wells, highly deviated wells or horizontal drains. In some cases, stopping the rotation can also make the rods stick against the wall of the hole, through a differential pressure effect, which hinders the continuation of the drilling.
Other techniques, currently developed, aim at implementing systems that make it possible to control the inclination and azimuth orientation of the drilling, while maintaining the rotation of the drill string from the surface, which is the underlying principle of the traditional rotary drilling. The most evolved (and the most complex) systems called RSS, xe2x80x9cRotary Stecrable Systemxe2x80x9d, make it possible to generate a substantially lateral force against the drill bit, using pistons that rest on the wall of the well (technique called xe2x80x9cPush The Bitxe2x80x9d) or to slightly pivot the drill bit in any direction, by bending the drill shaft upstream from the drill bit. The complexity of said systems is linked to the activation mechanism, as well as to the device that controls and commands the orientation of the action.
At the same time, the development of the directional behavior codes of the string in traditional rotary drilling, using stabilized rotary strings, has made it possible to highlight the influence of a certain number of parameters linked to the geometry and the mechanical characteristics of the string, that have a significant influence on the directional answer of the drilling system.
Indeed, if the well has a significant inclination, the string, under the effect of gravity, rests on the lower part of the hole. It takes on a deformed profile (abbreviated as xe2x80x9cdistortionxe2x80x9d), that can be controlled by varying the resting points, meaning by acting on the position and the diameter of the stabilizers, whose role is to more or less center the drill collars in the hole. For a specific distortion of the string, we know the orientation of the lateral force the drill bit, which is, to simplify matters, either pointed upward, or pointed downward, from the direction of gravity. Experience has shown that any traditional rotary string that transmits a lateral force with a large enough module and directed upward to the drill bit will develop, in a consolidated formation, a tendency called xe2x80x9cupwardxe2x80x9d (also called xe2x80x9cbuild-up tendencyxe2x80x9d), whose final effect will be an increase in the inclination of the well as the drilling is carried out. Conversely, any traditional rotary string that transmits a lateral force directed downward and with a rather large module to the drill bit will develop, in a consolidated formation, a tendency called xe2x80x9cfallingxe2x80x9d (also called xe2x80x9cdrop-off tendency), whose final effect will be a reduction of the inclination of the well as the drilling is carried out.
A third behavior can be added to these two and relates to the use of rotary drilling strings in straight sections (called xe2x80x9cslant sections), that still today make up a large portion of the drilled lengths in modem deviated wells. Indeed, experience has also shown that any traditional rotary string subjected to a force that is lateral to the drill bit, directed either upward or downward, and with a low module (or even a non existent module) develops, in a consolidated formation, a tendency called xe2x80x9cneutralxe2x80x9d (also called xe2x80x9clock-up tendencyxe2x80x9d), whose final effect is to maintain the inclination of the well as the drilling is carried out.